Single-crystal structure of the spicy capsaicin.

The crystal structure of capsaicin (CHNO), or trans-8-methyl-N-vanillylnon-6-enamide, the natural product responsible for the spiciness of chilli peppers, was determined using low-temperature single-crystal X-ray diffraction. The reported crystal structure is in good agreement with previous determinations based on powder X-ray diffraction data. The localization and free refinement of all H atoms revealed that each capsaicin molecule is hydrogen bonded to four other molecules, with the O-H and N-H groups acting as hydrogen-bond donors, and the C=O group serving as a bifurcated hydrogen-bond acceptor.